1. Field of the Invention
The present invention relates to a process for growing a thin metallic film and an apparatus therefor. Particularly, the present invention relates to a process and apparatus for growing a thin metallic film, which is suitable as metallic wiring in a semiconductor integrated circuit.
2. Description of the Prior Art
Several methods have been proposed for depositing copper or gold, each of which has a high migration resistance and a low electric resistance, instead of aluminum which is a conventional wiring material, in a semiconductor integrated circuit by chemical vapor deposition (CVD).
These methods use as a starting material .beta.-ketonato type materials such as copper or gold acetylacetonate or hexafluoroacetylacetonate, cyclopentadienyl type materials such as cyclopentadienyltriethylphosphines, inorganic compounds such as copper nitrate and copper chloride, and the like, and decompose the starting material by heat, plasma, light or the like to deposit the metal contained in the starting material.
.beta.-Ketonato type materials have a relative high vapor pressure and are stable at room temperature, and therefore there have been many proposals for CVD deposition of copper utilizing them.
CVD methods utilizing thermal decomposition include the following known methods.
CVD methods for deposition of copper by thermal decomposition of copper acetylacetonate in an inert gas such as argon, nitrogen or carbon dioxide are disclosed in "METAL COATED DIELECTRICS AND METHOD FOR PRODUCING SAME", U.S. Pat. No. 2,833,676 to Heibel et al. (1954); "METHOD OF BONDING ARTICLES", U.S. Pat. No. 2,760,261; and "GAS PLATING METAL OBJECTS WITH COPPER ACETYLACETONATE ", U.S. Pat. No. 2,704,728 to Pawlyk et al. (1952).
A method for thermally decomposing hexafluoroacetylacetonate with a reducing gas such as hydrogen is disclosed in "VAPOR-PLATING METALS FROM FLUOROCARBON KETO METAL COMPOUNDS", U.S. Pat. No. 335,627 to Moshier et al., (1964).
A method for thermally decomposing a hydrate of hexafluoroacetylacetonate in hydrogen is disclosed in "Vapor Deposition of Metal by Hydrogen Reduction of Metal Chelates" J. Electrochem. Soc., Vol. 112, No. 11, p.1123 to Hemart et al. (1965); and the like.
Further, the following methods are known as methods for selectively growing metals on substrates using thermal CVD.
A selective growing method utilizing a competitive progress of a growing reaction along with an etching reaction by addition of an etching gas is disclosed in "METHOD OF SELECTIVE CHEMICAL VAPOR DEPOSITION", U.S. Pat. No. 3,697,342 to Cuomo et al. (1970).
A selective growing method utilizing a different substrate without an etching reaction by optimization of conditions in reduced pressure CVD is disclosed in "PROCESS FOR GROWING THIN METALLIC FILM AND APPARATUS THEREFOR", U.S. Pat. application Ser. No. 07/354,158, Awaya et al.
As a method utilizing plasma reaction, there has been proposed a method for depositing copper by decomposition of copper hexafluoroacetylacetonate with a glow discharge in hydrogen as disclosed in "Thin Copper Film by Plasma CVD Using Copper- Hexafluoro-Acetylacetonate", Oehr, Appl. Phys. A45, 1988, p. 151-154.
Also, as methods utilizing a photochemical reaction, there have been proposed a method for decomposing hexafluoroacetylacetonate or its hydrate with light and heat using a converged argon ion laser and a method for photochemically decomposing hexafluoroacetylacetonate in an alcohol atmosphere using a high pressure mercury lamp or excimer laser (cf. "Process for depositing metallic copper" European Patent Application Publication No. 0135 179 A1, Houle, 1983, "Surface processes leading to carbon contamination of photochemically deposited copper films", Houle, J. Vac. Sci. Technol. A4 (6), 1986, p. 2452-2458, and "Photochemical generation and deposition of copper from a gas phase precursor", Jones, Appl. Phys. Lett. 46 (1), 1985, p.97-99).
Also, as a method using cyclopentadienyl type materials, there have been proposed a method for depositing copper by decomposition of cyclopentadienyltriethylphosphine with heat and a method for photochemically decomposing cyclopentadienyltriethylphosphine using laser light ("Method for Chemical Vapor Deposition of Copper, Silver, and Gold Using a Cyclopentadienyl Metal complex" European Patent application Publication No. 0297 348 A1, Beach).
As methods using an inorganic compound, there have been proposed a method for thermally decomposing copper nitrate as disclosed in "DYNAMIC PYROLYTIC PLATING PROCESS", U.S. Pat. No. 2,576,289, 1951, and a method for decomposing copper nitrate utilizing thermal decomposition and plasma as disclosed in "METHOD OF FORMING A COPPER FILM BY CHEMICAL VAPOR DEPOSITION", U.S. Pat. No. 4,842,891, 1989.
The above-described method for forming a copper film by thermal decomposition of .beta.-ketonato type materials is advantageous in that the starting material is relatively stable and therefore easy to handle and enables selective growing by changing the substrate material. Hence, this method makes it possible to completely fill fine holes such as contact holes or through-holes in wirings of a semiconductor integrated circuit, and is a technique compatible with fine processing techniques.
In the above-described methods, however, there tend to occur protrusions and depressions of crystals or gaps in grain boundaries depending on the metal material used for the substrate, thus causing a problem when deposited films are used as wiring material. In addition, the above-described methods are difficult to apply to practical production steps for producing integrated circuits because growth rate under conditions where selective growing is realized is as low as 10 nm/min. When a hydrate of hexafluoroacetonate is used in the above-described methods, deposition of a film having good film quality is obtained. However, the hydrate used as a starting material gradually decomposes at evaporation temperature so that it is impossible to assure a stable supply of the starting material to a reaction chamber. Therefore, in this case too, there arises a problem in using the methods in production on an industrial scale.
On the other hand, in the methods for growing thin films by plasma CVD or by simultaneous use of light and heat using .beta.-ketonato type materials as a starting material, it is possible to form a deposited film which is smooth and has a low resistivity. However, it is difficult to effect selective growth by changing substrate material and coverage in stepped portions is insufficient. Hence, it is difficult to apply the method for growing thin films utilizing plasma CVD to fine wiring formation.
Also, in the methods for growing thin films utilizing only a photochemical reaction, more specifically, methods for depositing metals by photochemically decomposing hexafluoroacetylaceotnate or its alcoholate in an alcohol atmosphere, the deposited film is an amorphous film containing therein 10% or more of carbon, thus failing to provide a good metal film deposition.